kather



Feb. 21, 1956 E. N. KATHER 2,735,959

TUNABLE MAGNETRON DEVICE Filed Oct. 6, 1949 2 Sheets-Sheet 1 /NVEN7U/? ERIC/f M M 71/51? T70/ZNE Y Feb. 21, 1956 v "E. N. KATHER 2,735,959

TUNABLE MAGNETRON DEVICE Filed Oct. 6, 1949 2 Sheets-Sheet 2 OUTPUT. 1 I

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United States PatentO TUNABLE MAGNETRON DEVICE Erich N. Kather, South Lincoln, Mass., assignor to Raytheon Manufacturing Company, Newton, Mass., a corporation of Delaware Application October 6, 1949, Serial No. 119,938

17 Claims. (Cl. 31539.61)

This application relates to electron discharge devices and more particularly to discharge devices of the tunable magnetron type.

In order to vary the frequencies of magnetron devices it has been found that elements may be inserted into the resonant cavities of the device to vary the resonance thereof, thereby changing the frequency of the device. The most effective elements for varying the resonant frequencies of the cavities are metallic elements. However, metallic elements have the disadvantage that eddy currents will be induced therein which create heat, thereby limiting the maximum power available from the device and also decreasing the over-all efficiency of the device.

Furthermore, when these elements are inserted toward the inner ends of the resonant cavities nearest the cathode to vary the capacitance of the cavities, eddy currents flowing in these elements will vary the inductance of the cavities in the opposite direction from the variation of the capacitance of the cavities, thereby tending to neutralize the tunning effect of the elements.

Applicant has discovered that, by eliminating the material in the tuning elements which would normally enter high current regions of the cavity, the eddy currents which are induced in the tuning elements may be substantially reduced. This results in both an increase in operating efficiency and an increase in the degree of tuning which may be produced.

It is well known that magnetrons may be tuned by simply tuning their resonant cavity structure, while holding both the magnetic field across the electron discharge path and the potential difference between the cathode and anode constant, but this procedure requires that the magnetron anode current vary with the wave length of operation.

In order to maintain both voltage and current constant, the magnetic field should be varied in accordance with the relationship B=magnetic field applied across the electron discharge path transverse to the direction of motion of the electrons.

V=the potential difference between the anode and cathode structure.

D=Allis parameter which is dependent on the design of the tube and is substantially proportional to the Wave length of operation of the magetron 7\.

ra=radius of the hole in the anode structure concentric with the cathode.

rc=radius of the cathode.

Since re and re are fixed by the geometry of the tube, and it is desired to operate with a constant voltage V, the expression reduces to:

2,735,959 Patented Feb. 21, 1956 B is proportional to D, and since D is proportional to A, B is proportional to A, or

where K is constant.

In order to vary the reluctance of the magnetic circuit, and hence the magnetic flux with the wave length of operating frequency, a movable magnetic pole is mechanically attached to the tuning structure such that, upon insertion of the tuning structure in the cavities of the cavity resonator, the gap between the movable magnetic pole and a fixed magnetic pole on the opposite side of the electron path is decreased, thereby increasing the magnetic flux applied across the electron path.

These and other advantages will become apparent as the description of a particular species progresses, reference being had to the accompanying drawing wherein:

Fig. 1 illustrates a longitudinal cross-sectional view of a magnetron incorporating this invention taken along line 11 of Fig. 2;

Fig. 2 illustrates a partially broken away, transverse cross-sectional view of the device shown in Fig. 1 taken along line 22 of Fig. l; and

Fig. '3 illustrates a perspective view of the novel tuning structure used in Figs. 1 and 2 utilizing applicants invention.

Referring now to Figs. 1 and 2, there is shown an anode structure 10 comprising an outer anode cylinder 11 which may be of any desired material, such as copper. Extending radially inwardly from the inner surface of the anode surface 11 is a plurality of anode elements 12 comprising substantially rectangular plates whose surfaces are parallel to the axis of cylinder 11.

In order to eliminate spurious oscillations in the anode structure, alternate anode members 12 are connected at their lower edges adjacent their inner ends by straps 13 in a well-known manner. The ends of the anode cylinder 11 are sealed by upper and lower end plates 14 and 15, respectively. Extending through an opening in lower end plate 15 and concentric with the axis of cylinder 11 is a lower magnetic pole piece 16, which may be of any magnetic material, such as iron or silicon steel. Pole piece 16 has a hole extending axially therethrough concentric with anode cylinder 11. Extending through this hole is a cathode structure 17 comprising a metallic cylinder 18 which extends upwardly past the inner ends of the anode members 12. Cylinder 18 has electron emissive material coated on the'outer surface thereof on the portion which is in proximity with the inner ends of the anode member 12. Cylinder 18 contains therein a heater coil 19 which may be insulated from cylinder 18 by a coating of insulating material, such as Alundum. The upper end of heater coil 19 is attached to cylinder 18 as at 20, for example, by welding and the lower end of heater coil 19 extends downwardly through cylinder 18 and is attached to a lead-in member 21 which extends through and is rigidly supported by an insulating seal, not shown, in a Well-known manner. Cathode cylinder 18 extends downwardly through the hole in pole piece 16, and is attached to a supporting tube 22 which is insulatingly sealed with respect to lower pole piece 16 in a well-known manner.

Upper end plate 14 has therein a hole concentric with cylinder 11 and through which extends an upper stationary pole piece 23. Pole piece 23 comprises a cylinder through which extends a movable pole piece 24, which snugly and slidably contacts the inner surface'of pole piece 23. Movable pole piece 24 has a recess 25 in its lower end which accommodates the upper end'of the cathode structure 17.

A vacuum seal is produced between movable pole piece 24' and end plate 14 by a diaphragm structure 26 described in greater detail in copending application, Serial No. 793,889, filed December 26, 1947 and now Patent No. 2,621,311.

Energy may be removed from the cavities between elements 12 in any well-known manner, for example, by means of a loop 27, one end of which is attached to a cylindrical member 28 threaded into cylinder 11 and the other end of which extends out through the wall of cylinder 11 coaxial and insulatingly sealed to member 28.

Attached to the lower end of movable pole piece 24 is a tuning structure 29 shown in greater detail in Pig. 3. Structure 29 comprises a cylindrical member 39 surrounding the lower end of pole piece 24 and rigidly attached thereto. Extending downwardly into the cavities defined by anode elements 12 is a plurality of tuning elements 32 rigidly attached to cylinder 30, one of said elements extending into each of the cavities defined by anode members 12. Each tuning element has a transverse cross section which is substantially V-shaped with the apex of the V adjacent and pointing toward cathode structure 17, and the legs of the V extending outwardly in close proximity with, but not touching, the surfaces of anode members 12. The material between the outer ends of the legs of the V has been removed by making a trapezoidal-shaped cut in the element. This produces a structure wherein substantially none of the metallic portions of the tuning elements extends into regions of the cavity where high currents are encountered, these regions being generally the portions of the cavity adjacent to the outer portion of the cylinder 11 and the middle portions of the cavity away from the walls formed by anode members 12. The result is that substantially no eddy currents are induced in the tuning elements and as a result there is very little effect on the inductive parameter of the cavities. Therefore, the capacitance change produced by insertion of the tuning elements is substantially unneutralized by changes in the inductance of the cavities, and also losses in the tuning element are substantially eliminated.

It may be seen that, by movement of the movable pole piece downwardly, the elements of the tuning structure 29 are inserted into the cavities formed by anode members 12 adjacent the inner ends thereof. Since the inner region of the cavities are highly capacitive due to the proximity of the anode members 12 to each other, insertion of the tuning elements effectively increases this capacity by varying the air-gap distance between adjacent anode members. This increase of the capacitance causes a decrease in the resonant frequencies of the cavities, thereby tuning the device. Since, as previously discussed, the required anode voltage and magnetic field relationship vary as a function of the frequency, it is necessary to vary either the anode voltage or the magnetic field to obtain optimum operating conditions over a wide range of frequencies. By moving one of the magnetic pole pieces, the magnetic field may be automatically varied to produce the correct operating conditions.

This completes the descriptions of the embodiment of the invention illustrated herein. However, many modifications thereof will become apparent to persons skilled in the art without departing from the spirit and scope of this invention. For example, other configurations of the anode structure and cavities might be used and other means for varying the magnetic field or anode voltage to produce the required operating conditions may be possible without departing from the spirit and scope of this invention. Therefore, applicant does not wish to be limited to the particular details of the species of the invention described herein except as defined by the appended claims.

What is claimed is:

1. An electron discharge device comprising an anode structure defining a cavity resonator which has a plurality of cavities, a cathode adjacent said structure, and

a tuning structure movably positioned with respect to said cavity resonator, an element of said tuning structure extending into each cavity of said cavity resonator, each tuning element comprising a rod positioned in the high capacity area of said cavity adjacent said cathode, said rod having metallic portions thereof adjacent the walls of said cavity and a portion thereof between said metallic portions which is void of metal.

2. An electron discharge device comprising an anode structure defining a cavity resonator which has a plurality of cavities, a cathode adjacent said structure, and a tuning structure movably positioned with respect to said cavity resonator, an element of said tuning structure extending into each cavity of said cavity resonator, each tuning element comprising a rod positioned in the high capacity area of said cavity adjacent said cathode, said rod having metallic portions thereof adjacent the walls of said cavity and having a space which is void of metal between said metallic portions.

3. An electron discharge device comprising an anode structure, said anode structure defining a cavity resonator comprising a plurality of cavities, a cathode adjacent said structure, a tuning structure movably positioned with respect to said cavity resonator, an element of said tuning structure extending into each cavity of said cavity resonator, said element comprising a rod having a V-shaped cross-section positioned in the high capacity area of said cavity adjacent the cathode and having the apex of the V pointed toward the cathode, a magnetic pole piece movable with respect to said cavity resonator and adjacent thereto, and means connected to said rod for moving said rod in conjunction with said tuning structure whereby variations of the magnetic fiux applied across the electron path of said discharge device are a function of variations in the resonant frequency of said cavity resonator.

4. An electron discharge device comprising an anode structure defining a cavity resonator which has a plurality of cavities, a cathode adjacent said structure, a tuning structure movably positioned with respect to said cavity resonator, an element of said tuning structure extending into each cavity of said cavity resonator, each tuning element comprising a rod positioned in the high capacity area of said cavity adjacent said cathode, said rod having metallic portions thereof adjacent the walls of said cavity and a portion thereof between said metallic portions which is void of metal, and a rod of magnetic material which is movable with respect to said cavity resonator, said tuning structure being rigidly attached to said magnetic rod.

5. An electron discharge device comprising an anode structure defining a cavity resonator which has a plurality of cavities, a cathode adjacent said structure, a tuning structure movably positioned with respect to said cavity resonator, an element of said tuning structure extending into each cavity of said cavity resonator, each tuning element comprising a rod positioned in the high capacity area of said cavity adjacent said cathode, said rod having metallic portions thereof adjacent the walls of said cavity and a portion thereof between said metallic portions which is void of metal, a rod of magnetic material which is movable with respect to said cavity resonator, and means connected to said rod for moving said magnetic rod in conjunction with said tuning structure.

6. An electron discharge device comprising an anode structure defining a cavity resonator which has a plurality of cavities, a cathode adjacent said structure, and a tuning structure movably positioned with respect to said cavity resonator, an element of said tuning structure extending into each cavity of said cavity resonator, each tuning element comprising a rod positioned in the high capacity area of said cavity adjacent said cathode, said rod having a first electrically conductive member adjacent said cathode, and a plurality of thin electrically conductive members electrically contacting said first member and extending along the walls of said cavity in close proximity therewith.

7. An electron discharge device comprising an anode structure defining a cavity resonator which has a plurality of cavities, a cathode adjacent said structure, and a tuning structure movably positioned with respect to said cavity resonator, an element of said tuning structure extending into each cavity of said cavity resonator, each tuning element comprising a rod, said rod having a first electrically conductive member adjacent said cathode, and a plurality of thin electrically conductive members electrically contacting said first member and extending along the walls of said cavity in close proximity therewith.

8. An electron discharge device comprising an anode structure defining a cavity resonator which has a plurality of cavities, a cathode adjacent said structure, a tuning structure movably positioned with respect to said cavity resonator, an element of said tuning structure extending into each cavity of said cavity resonator, each tuning element comprising a rod positioned in the high capacity area of said cavity adjacent said cathode, said rod having a first electrically conductive member adjacent said cathode, and a plurality of thin electrically conductive members electrically contacting said first member and extending along the walls of said cavity in close proximity therewith, and a rod of magnetic material which is movable with respect to said cavity resonator, said magnetic rod being movable in conjunction with said tuning structure.

9. An electron discharge device comprising an anode structure, said anode structure defining a cavity resonator comprising a plurality of cavities, a cathode adjacent said structure, a tuning structure axially movably positioned with respect to said cavity resonator, an element of said tuning structure extending into each cavity of said cavity resonator, said element comprising a rod having a V-shaped cross-section positioned in the high capacity area of said cavity adjacent the cathode and having the .apex of the V pointed toward the cathode, a rod of magnetic material movably mounted with respect to said cavity resonator, and means connected to said rod for moving said rod in conjunction with said tuning structure.

10. An electron discharge device comprising an anode :structure, said anode structure defining a cavity resonaztor comprising a plurality of cavities, a cathode adjacent :said structure, a tuning structure axially movably positioned with respect to said cavity resonator, an element of said tuning structure extending into each cavity of said cavity resonator in the high capacity region thereof, said element having substantially no eifect on the inductance of said cavity, and means for varying the magnetic field applied across the electron paths of said device comprising a rod of magnetic material positioned coaxial with said cavity resonator and movable with respect to said cavity resonator rigidly attached to said tuning structure.

11. An electron discharge device comprising an anode structure, a cathode spaced from said anode structure, said anode structure comprising a plurality of cavities, a tuning structure movably positioned adjacent said cavities, means for varying the magnetic flux in said cavities comprising a rod of magnetic material movable with respect to said cavities and positioned adjacent thereto, and means connected to said rod and tuning structure for moving said rod in conjunction with said tuning structure for varying the magnetic flux applied across the electron paths of said discharge device with variations in the operating frequency of said device.

12. An electron discharge device comprising an anode structure and a cathode adjacent said anode structure, said anode structure defining a cavity resonator, a tuning structure movably positioned adjacent said cavity resonator, means for varying the magnetic flux in said cavity resonator comprising a rod of magnetic material movable with respect to said cavity resonator and positioned adjacent thereto, and means connected to said rod and tuning structure for moving said rod in conjunction with said tuning structure.

13. An electron discharge device comprising an electron source, an anode structure spaced from said electron source, said anode structure defining a cavity resonator comprising a plurality of cavities, means for directing electrons from said source along paths adjacent said anode structure comprising means for producing a magnetic field extending through said paths substantially perpendicular thereto, means for varying said magnetic field comprising a rod of magnetic material movable with respect to said anode structure and positioned adjacent thereto, and a tuning structure positioned adjacent said anode structure and rigidly secured with respect to said rod.

14. An electron discharge device comprising an electron source, an anode structure spaced from said source, said anode structure comprising a plurality of frequency responsive elements, means for directing electrons from said source along paths adjacent said anode structure comprising a magnetic circuit means for producing a magnetic field transverse to said paths, means adjacent said anode structure for substantially varying the reluctance of said magnetic circuit, means adjacent said anode structure for varying the operating frequency of said device, and means linked to the operating frequency varying means and to the magnetic circuit reluctance varying means for varying said magnetic field in conjunction with variations of the operating frequency of said device.

15. An electron discharge device comprising an anode structure having a plurality of cavities, an electron emissive cathode spaced from said anode structure, a tuning structure movably positioned adjacent said cavities and including at least one tuning element extending into at least one of said cavities for altering the operating frequency of said device, means for directing electrons from said cathode along paths adjacent said anode comprising means for producing a magnetic field extending through said paths substantially perpendicularly thereto, said magnetic field producing means including a fixed magnetic pole piece and a movable magnetic pole piece mechanically attached to said tuning structure, and means responsive to movement of said tuning structure for varying the gap between said pole pieces in accordance with .alterations in the operating frequency of said device.

16. An electron discharge device comprising an anode structure having a plurality of cavities, an electron emissive cathode spaced from said anode structure, a tuning structure movably positioned adjacent said cavities for altering the operating frequency of said device and including at least one tuning element extending into at least one of said cavities, each tuning element being positioned in the high capacity area of said cavity adjacent the cathode and having metallic portions adjacent the walls of said cavity and a portion thereof between said metallic portions which is void of material, means for directing electrons from said cathode along paths adjacent said anode comprising means for producing a magnetic field extending through said paths substantially perpendicularly thereto, said magnetic field producing means including a fixed magnetic pole piece and a movable magnetic pole piece mechanically attached to said tuning structure, means for altering the degree of insertion of said tuning structure into said cavities, and means responsive to movement of said tuning structure for varying the gap between said pole pieces in accordance with alterations in the operating frequency of said device.

17. An electron discharging device comprising an anode structure having a plurality of cavities, an electron emissive cathode spaced from said anode structure, a tuning structure movably positioned adjacent said cavities for altering the operating frequency of said device and including at least'one tuning element extending into at least one of said cavities, means for directing electrons from said cathode along paths adjacent said anode comprising means for producing a magnetic field extending through said paths substantially perpendicularly thereto, said magnetic field producing means including a fixed magnetic pole piece and a movable magnetic pole piece mechanically attached to said tuning structure, means for altering the degree of insertion of said tuning structure into said cavities whereby the operating frequency is altered inversely with the magnetic field intensity.

References Cited in the file of this patent UNITED STATES PATENTS Steele, Jr Sept. 21, 1948 Sonkin Oct. 5, 1948 Litton Jan. 31, 1950 Nelson Feb. 7, 1950 Brown Aug. 26, 1952 La Rue Dec. 9, 1952 

